Organic Chemistry II Exam Questions and Rationales, Exams of Chemistry

Download Organic Chemistry II Exam Questions and Rationales and more Exams Chemistry in PDF only on Docsity! AS.030.206 Organic Chemisry II LATEST EXAM w/ RATIONALES 2024 1. Which reagent would be most suitable for the following organic synthesis reaction? Question: In a synthesis reaction to form an ester, an alcohol reacts with a carboxylic acid. Which reagent could be used to catalyze this reaction? a) Hydrochloric acid (HCl) b) Sodium hydroxide (NaOH) c) Sulfuric acid (H2SO4) d) Concentrated sulfuric acid (H2SO4) Answer: d) Concentrated sulfuric acid (H2SO4) Rationale: Concentrated sulfuric acid functions as a catalyst in the esterification reaction by protonating the carboxylic acid, making it more susceptible to nucleophilic attack by the alcohol, thus promoting ester formation. 2. Which synthetic method would be most appropriate to prepare a tertiary alcohol from a ketone? Question: Which synthetic method is suitable to convert a ketone into a tertiary alcohol? a) Oxidation reaction b) Grignard reaction c) Reduction reaction d) Condensation reaction Rationale: Protecting groups are temporary modifications of functional groups in a molecule, used to selectively react or protect specific groups while preventing unwanted reactions elsewhere in the molecule. 6. Which method is commonly employed to install a halogen atom into an organic molecule? Question: Which method is commonly used to install a halogen atom (e.g., chlorine, bromine) into an organic molecule? a) Substitution reaction b) Decarboxylation reaction c) Elimination reaction d) Aldol condensation reaction Answer: a) Substitution reaction Rationale: Substitution reactions, such as nucleophilic substitution (SN1 or SN2), are frequently used to introduce halogens into organic molecules. These reactions involve the replacement of a functional group or an atom with a halogen atom. 7. Which compound serves as a primary carbon source in carbene reactions? Question: In carbene reactions, which compound primarily serves as a source of carbon? a) Aldehyde (RCHO) b) Ketone (RCOR') c) Carboxylic acid (RCOOH) d) Diazomethane (CH2N2) Answer: d) Diazomethane (CH2N2) Rationale: Diazomethane (CH2N2) is commonly used as a source of carbenes (CH2) in organic synthesis. The carbon- carbon double bond in the carbene can subsequently react with other molecules. 8. Which reagent would be most suitable to convert an alcohol into an alkene via dehydration? Question: Which reagent is commonly used to convert an alcohol into an alkene via dehydration? a) Sodium hydroxide (NaOH) b) Sulfuric acid (H2SO4) c) Ethylene (C2H4) d) Copper oxide (CuO) Answer: b) Sulfuric acid (H2SO4) Rationale: Sulfuric acid is frequently employed to dehydrate alcohols, selectively removing a molecule of water to generate an alkene through an elimination reaction. 9. Which reaction mechanism best describes the formation of a benzene ring? Question: The formation of a benzene ring can be best explained by which reaction mechanism? a) Electrophilic aromatic substitution b) Nucleophilic substitution c) Addition reaction d) Elimination reaction Answer: a) Electrophilic aromatic substitution Rationale: The formation of a benzene ring involves the replacement of a hydrogen atom on the ring by an electrophile. This substitution reaction, known as electrophilic aromatic substitution, is a characteristic reaction of aromatic compounds. 10. Which reagent is commonly used in the Suzuki coupling reaction? Question: In the Suzuki coupling reaction, which reagent is commonly used as a source of the nucleophilic coupling partner? a) Organohalide (R-X) b) Grignard reagent (RMgX) c) Organotin compound (R-SnR'3) ether, a nucleophilic substitution reaction occurs. One alcohol molecule acts as the nucleophile, attacking the other alcohol molecule and displacing the -OH group, forming the ether. 14. Which synthetic method is commonly used to introduce an alkyl group into an aromatic ring? Question: Which synthetic method is commonly used to introduce an alkyl group into an aromatic ring? a) Electrophilic aromatic substitution b) Nucleophilic substitution c) Reductive amination d) Elimination reaction Answer: a) Electrophilic aromatic substitution Rationale: Electrophilic aromatic substitution reactions are used to introduce alkyl substituents onto aromatic rings. This reaction involves the substitution of a hydrogen atom on the aromatic ring with an electrophile. 15. Which reagent can be used to convert an alkene into an alcohol by oxymercuration-demercuration? Question: Which reagent is commonly used for the oxymercuration-demercuration reaction, which converts an alkene into an alcohol? a) Sodium borohydride (NaBH4) b) Potassium permanganate (KMnO4) c) Mercury(II) acetate (Hg(OAc)2) d) Lithium aluminum hydride (LiAlH4) Answer: c) Mercury(II) acetate (Hg(OAc)2) Rationale: The oxymercuration-demercuration reaction employs mercury(II) acetate as a reagent to add a hydroxy group (OH) to an alkene, converting it into an alcohol. The subsequent demercuration step removes the mercury atom. B: Question 1: Which of the following reagents is commonly used for the oxidation of primary alcohols to aldehydes? A. PCC (pyridinium chlorochromate) B. KMnO4 (potassium permanganate) C. NaBH4 (sodium borohydride) D. LiAlH4 (lithium aluminum hydride) Answer: A. PCC (pyridinium chlorochromate) Rationale: PCC is a mild and selective oxidizing agent that converts primary alcohols to aldehydes without further oxidation to carboxylic acids. Question 2: In the Friedel-Crafts acylation reaction, which of the following reagents is commonly used as the acylating agent? A. Acetic anhydride B. Acetyl chloride C. Formic acid D. Acetone Answer: B. Acetyl chloride Rationale: Acetyl chloride is the most commonly used acylating agent in the Friedel-Crafts acylation reaction due to its reactivity and ability to form ketones from aromatic compounds. Question 3: Which of the following is a commonly used method for the reduction of carboxylic acids to primary alcohols? A. Wolff-Kishner reduction B. Clemmensen reduction C. LiAlH4 reduction D. NaBH4 reduction Answer: A. Wolff-Kishner reduction Rationale: The Wolff-Kishner reduction is a widely used method for the conversion of carboxylic acids to primary alcohols under high-temperature conditions. Question 4: When performing a Grignard reaction, which of the following solvents is typically used due to its inertness towards the Grignard reagent? A. Diethyl ether Question 9: Which of the following methods is commonly employed for the conversion of an alkyl halide to an alkene? A. E2 elimination B. E1 elimination C. SN1 substitution D. SN2 substitution Answer: A. E2 elimination Rationale: E2 elimination is a common method for the conversion of alkyl halides to alkenes, involving the removal of a proton from a beta-carbon and the simultaneous elimination of the leaving group. Question 10: In the synthesis of an ether from two alcohols, which of the following reagents is commonly used as the catalyst for the reaction? A. H2SO4 (sulfuric acid) B. HCl (hydrochloric acid) C. NaOH (sodium hydroxide) D. H3PO4 (phosphoric acid) Answer: A. H2SO4 (sulfuric acid) Rationale: Sulfuric acid is commonly used as a catalyst in the synthesis of ethers from two alcohols, facilitating the dehydration reaction to form the ether product. Question 11: Which of the following reagents is commonly used for the reduction of nitro groups to primary amines? A. H2 (hydrogen) with Pd/C (palladium on carbon) B. Fe/HCl (iron with hydrochloric acid) C. NaBH4 (sodium borohydride) D. LiAlH4 (lithium aluminum hydride) Answer: A. H2 (hydrogen) with Pd/C (palladium on carbon) Rationale: The reduction of nitro groups to primary amines is commonly achieved using hydrogen in the presence of a palladium catalyst. Question 12: In the synthesis of a nitrile from a primary amine, which of the following reagents is commonly used in the reaction? A. Phosphorus tribromide (PBr3) B. Thionyl chloride (SOCl2) C. Acetic anhydride D. Hydrogen cyanide (HCN) Answer: D. Hydrogen cyanide (HCN) Rationale: Hydrogen cyanide is commonly used in the synthesis of nitriles from primary amines through the process of nitrile formation. Question 13: Which of the following reagents is commonly used for the oxidation of aldehydes to carboxylic acids? A. KMnO4 (potassium permanganate) B. PCC (pyridinium chlorochromate) C. NaBH4 (sodium borohydride) D. LiAlH4 (lithium aluminum hydride) Answer: A. KMnO4 (potassium permanganate) Rationale: Potassium permanganate is a strong oxidizing agent that can effectively oxidize aldehydes to carboxylic acids. Question 14: When performing a nucleophilic addition reaction of a grignard reagent with a carbonyl compound, which of the following functional groups is formed as the product? A. Alcohol B. Ketone C. Alkene D. Amine Answer: A. Alcohol Rationale: The nucleophilic addition of a Grignard reagent with a carbonyl compound results in the formation of an alcohol product through the addition of the grignard reagent to the carbonyl carbon. Question 15: In the synthesis of an amide from a carboxylic acid and an amine, which of the following reagents is commonly used to drive the reaction to completion? A. Thionyl chloride (SOCl2) B. Acetic anhydride C. H2SO4 (sulfuric acid) D. NH3 (ammonia) Answer: A. Thionyl chloride (SOCl2) Rationale: Thionyl chloride is commonly used to drive the amidation reaction to completion by converting the carboxylic acid to an acid chloride, which then reacts with the amine to form the amide product. c) Aldol condensation d) All of the above *Answer: d) All of the above* Rationale: Grignard reaction involves the reaction of an organomagnesium halide (Grignard reagent) with an electrophile, such as an aldehyde, ketone, or ester. Friedel- Crafts alkylation involves the reaction of an alkyl halide with an aromatic ring in the presence of a Lewis acid catalyst, such as AlCl3. Aldol condensation involves the reaction of two aldehydes or ketones under basic or acidic conditions, forming a beta-hydroxy carbonyl compound (aldol) and then eliminating water to form an alpha-beta unsaturated carbonyl compound. 5. Which of the following compounds can be synthesized from cyclohexanone using the Robinson annulation reaction? a) 6-methylcyclohex-2-enone b) 2-methylcyclohexanone c) 4-methylcyclohex-2-enone d) 2-methylcyclohex-2-enone *Answer: c) 4-methylcyclohex-2-enone* Rationale: Robinson annulation is a two-step reaction that involves a Michael addition followed by an intramolecular aldol condensation. The Michael addition involves the attack of a nucleophilic enolate on an alpha-beta unsaturated carbonyl compound, forming a 1,5-dicarbonyl compound. The intramolecular aldol condensation involves the cyclization of the 1,5-dicarbonyl compound by eliminating water, forming a six-membered ring with a double bond. To synthesize 4-methylcyclohex-2-enone from cyclohexanone, the enolate of cyclohexanone can react with methyl vinyl ketone in the Michael addition, and then cyclize in the aldol condensation. 6. Which of the following reagents can be used to convert an aldehyde to a carboxylic acid? a) KMnO4 b) LiAlH4 c) PCC d) NaBH4 *Answer: a) KMnO4* Rationale: KMnO4 is a strong oxidizing agent that can oxidize aldehydes to carboxylic acids. LiAlH4 and NaBH4 are strong reducing agents that can reduce aldehydes to primary alcohols. PCC is a mild oxidizing agent that can oxidize primary alcohols to aldehydes, but not further to carboxylic acids. 7. Which of the following reactions can be used to synthesize 2,4-dimethylpentane from 2-methylpropene? a) Hydrohalogenation b) Halogenation c) Hydration d) All of the above *Answer: d) All of the above* Rationale: Hydrohalogenation is the addition of a hydrogen halide (HX) across a double bond, forming an alkyl halide. Halogenation is the addition of a halogen (X2) across a double bond, forming a vicinal dihalide. Hydration is the addition of water (H2O) across a double bond, forming an alcohol. All of these reactions can be used to synthesize 2,4-dimethylpentane from 2-methylpropene by adding two carbon atoms to the double bond and then reducing the halogen or hydroxyl group to a hydrogen atom. 8. Which of the following statements is true about the Diels-Alder reaction? a) It is a cycloaddition reaction that forms a six-membered ring from a diene and an alkene. b) It is a cycloelimination reaction that forms a diene and an alkene from a six-membered ring. c) It is a cycloaddition reaction that forms a four-membered ring from a diene and an alkyne. d) It is a cycloelimination reaction that forms a diene and an alkyne from a four-membered ring. *Answer: a) It is a cycloaddition reaction that forms a six- membered ring from a diene and an alkene* Rationale: The Diels-Alder reaction is a [4+2] cycloaddition reaction that involves the reaction of a conjugated diene (four pi electrons) and an alkene (two pi electrons), forming a six-membered ring with one or two double bonds. The diene must be in the s-cis conformation for the reaction to occur. The alkene acts as a dienophile (diene lover) and must have electron-withdrawing groups to increase its electrophilicity. 9. Which of the following synthetic methods can be used to form carbon-carbon bonds between two different aromatic rings?